This invention relates to an electromagnetic pump of the type utilized to feed fuel to a motor car engine.
A prior art electromagnetic pump of the type referred to above comprises a vessel made up of a U shaped yoke made of such magnetic material as iron and steel, and a U shaped housing adapted to cover the opening of the yoke. Mechanical and electrical component elements of the pump are disposed in the pump vessel. One example of such electromagnetic pump is disclosed in U.S. Pat. No. 3,400,663. An electromagnetic pump disclosed in this U.S. patent comprises a yoke having opposed legs, and a non-magnetic sleeve containing a movable member of the pump, that is a plunger, which extends through openings of the legs, the opposite ends of the sleeve being supported by inlet and outlet fixtures threaded in respective openings. A bobbin wound with an exciting coil is received in a space between the two legs of the yoke to surround the sleeve with the exciting coil. On one side of the bobbin is disposed a printed circuit board containing such electronic component parts as resistors and diodes which constitute an oscillator together with a transistor. The transistor is mounted on the outside of the housing and connected to the printed circuit board by wires extending through openings of the housing. The oscillator supplies pulsating current to the exciting coil. The plunger is reciprocated in the plunger by the electromagnetic force created by the exciting coil and a return spring so as to feed fluid from an inlet passage in the inlet fixture to an outlet passage in the outlet fixture.
In most cases, since such an electromagnetic pump is mounted on the outside of a car body, particularly beneath its floor, the transistor mounted on the outside of the housing is often damaged by flying stones when the vehicle is in motion. Furthermore, water and mud accumulate on the electromagnetic pump and enter into the inside thereof through a joint between the yoke and the housing or openings for connecting the transistor, thus damaging various component parts. In extremely cold areas, rock salt is sprinkled on roads for the purpose of preventing freezing. When a motor car runs on such roads, a powder of rock salt is deposited on the electromagnetic pump whereby brine enters into the interior of the electromagnetic pump to electrolytically etch such conductive parts as terminals of circuit elements and copper wires of the coil which are at different potentials, thereby causing incomplete contact or breakage of the wire. Moreover, as a grounding lead wire extending from the inside of the electromagnetic pump is mounted on the transistor by a screw, these portions are particularly damaged.
For this reason, in a prior art electromagnetic pump a sealing agent was applied to gaps on the outside, for example a joint between the yoke and the housing, and a joint between the transistor and the housing, for preventing water and brine from entering into the electromagnetic pump. However, since there are many portions at which the sealing agent must be coated all around the electromagnetic pump and since it is difficult to apply the sealing agent to stepped portions, the coating operation is not only troublesome but also requires large labor and time factors and a large quantity of the sealing agent.
Another approach to this problem is disclosed in U.S. Pat. No. 3,492,619 in which a foamed material, for example, polyurethane foam is filled in an electromagnetic pump for the purpose of sealing the same. However, certain foamed material can not completely fill the interior of the pump, or does not adhere well to plastics so that it peels off. Thus, when the foamed material fails to completely fill the pump, voids exist which result in the undesired electrolytic etching noted above. Moreover, the adhesion of the foamed material to component elements of the pump is poor, thus causing the foam to peel off, resulting in electrolytic etching.